// Problem 15: Lattice paths
// Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom right corner.
// How many such routes are there through a 20×20 grid?
// --------
// In fact, the problem is the permutation of 20 R(ight) and 20 D(own).
// 40!/20!/20!=40*39*38*...*21/20!=2^10*39*37*35*33*31*29*27*25*23*21/10!
// [code python]
// import math
// print(math.factorial(40)/math.factorial(20)/math.factorial(20))
// [/code]

package main

import (
	"fmt"
)

func p015() int {
	ans := 4 * 5 * 7 * 23 * 29 * 31 * 33 * 37 * 39
	fmt.Println("Problem 015:", ans)
	return ans
}
